Background Currently, there is no consensus on the effect of obstructive sleep apnea on male serum testosterone levels. This systematic review and meta‐analysis aimed to determine the association between obstructive sleep apnea and male serum testosterone level. Methods The literature related to obstructive sleep apnea and male serum testosterone in the PubMed, Embase, and Cochrane Library databases were searched from their inception to June 10, 2021. Data were pooled using the Stata 15 software. We performed a subgroup analysis of studies after matching the age and body mass index, as well as according to the severity of obstructive sleep apnea. Results Eighteen studies involving 1823 men were included in the systematic review and meta‐analysis. A significant inverse association between obstructive sleep apnea and male serum testosterone (SMD = −0.76; 95% CI: −1.18, −0.33; p = 0.001) was found. After adjusting for age and body mass index, this inverse association still existed (SMD = −0.8; 95% CI = −1.41, −0.18, p = 0.012). According to the subgroup analysis of obstructive sleep apnea severity, our results showed that serum testosterone was not significantly decreased in mild (SMD = −0.58; 95% CI = −1.88, 0.73, p = 0.386) and moderate obstructive sleep apnea patients (SMD = −0.94; 95% CI = −2.04, 0.15, p = 0.092), whereas it was significantly reduced in patients with severe obstructive sleep apnea (SMD = −1.21; 95% CI = −2.02, −0.41, p = 0.003). Conclusions Obstructive sleep apnea is inversely associated with male serum testosterone levels, independent of body mass index and age. Notably, the severity of obstructive sleep apnea is also correlated with male serum testosterone, which is significantly reduced in patients with severe obstructive sleep apnea.

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Antioxidant supplementation has been identified as an important intervention for subfertile men. However, the effectiveness of different antioxidants in improving sperm quality remains unclear. In this study, a network meta-analysis (NMA) was designed to evaluate the effects of different antioxidants on sperm quality parameters in subfertile men. Published randomized controlled trials (RCTs) of antioxidants in subfertile men were searched in the PubMed, Embase, and Cochrane Library databases from inception to January 31, 2021. Eight antioxidants (folic acid, zinc, vitamin E, carnitine, selenium, coenzyme q10 [CoQ10], N-acetylcysteine, and vitamin C) and a placebo (control) were included in our study. A Bayesian NMA with random effects was performed for each outcome (sperm concentration, sperm motility, and sperm morphology); the surface under the cumulative ranking curves (SUCRAs) for the effectiveness of each intervention was applied to identify the optimal intervention. Eighteen studies with 1,790 subfertile men were included in the study. CoQ10 elicited a significant increase in sperm concentration (mean difference [MD] = 5.95; 95% confidence interval [CI] 0.05, 10.79) compared with the placebo; it achieved the highest rank in efficacy among all the antioxidants (SUCRA: 79.4%). With regard to sperm motility, carnitine (MD = 12.43; 95% CI 4.07, 20.26) and CoQ10 (MD = 7.33; 95% CI 0.35, 14.17) showed significant beneficial effects compared with the placebo; the efficacy of carnitine was the highest among all the antioxidants (SUCRA: 88.7%). With regard to sperm morphology, the efficacy of vitamin C tended to be the highest (SUCRA: 93.6%), although it did not show significant beneficial effect (MD = 7.73; 95% CI -0.94, 16.33) compared with the placebo. Overall, for subfertile men, CoQ10 and carnitine interventions showed better effectiveness in increasing sperm concentration and sperm motility, respectively. Significance The effectiveness of different antioxidants in improving sperm quality in subfertile men remains unclear. To the best of our knowledge, this is the first study to compare the effectiveness of different antioxidants on sperm quality parameters in subfertile men.